"… and a few years later Newton wrote in the Principia (Book I, section XIV): 'For it is now certain from the phenomena of Jupiter's satellites, confirmed by the observations of different astronomers, that light is propagated in succession (NOTE: I think this means at finite speed) and requires about seven or eight minutes to travel from the sun to the earth.'"

"The meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second."

3.00 × 108 m/s

Light, which is a form of electromagnetic wave, is a phenomenon that has puzzled
scientists for centuries. It was originally believed that the speed of light was
not constant. Then in 1676 a Danish astronomer named Ole Romer made one of the
first theories for a fixed value, c, the speed of light through free space. He
theorized that, from watching the eclipse patterns of Jupiter and its moon, Io,
that light travels at a finite speed due to the fact that the eclipses were seen
from earth at different times than they actually occurred. The occurred latest
when Io was furthest from earth and earliest when Io was closest to earth. This
was due to the time required for the light to travel from Io to the earth's surface.

Presently, the speed of light has a fixed value of 299,792,458 m/s.
Using Maxwell's equations, a relationship

can be derived that relates the speed of light to the fundamental constants
ε0 and μ0,
which are the vacuum permitivity and the permeability of free space. The speed
of light can be defined as the speed it takes light to travel one meter in 1/299,792,458
of a second.

"The equations do not allow light to halt yet continue to undulate. If light were to remain, thought Einstein, it must always travel at 186,000 miles per second even as seen by an observer moving at the same speed (or at any speed, in any direction); to the confusion of our ingrained visceral knowledge, a rider on a light beam can never catch an adjacent beam, although he too moves at the speed of light."

The speed of light is so far the fastest thing known to man. Light is an electromagnetic
wave. All electromagnetic waves from radio waves to x-rays travel at the speed
of light. Originally the speed of light was thought to be infinite. Every century
since the early 17th scientists have been perfecting the measurement of the value
of the speed of light. Now modern electronic methods have improved this accuracy
to a point that it has been given a set value. In 1983, the International Committee
on Weights and Measurements decided to make the speed of light a defined quantity:
299 792 458 m/s (although for most calculations 3.00 × 108 m/s
is sufficient).

It is said that the speed of light in a vacuum is the limiting velocity for
material particles, and that no particle can be accelerated from rest to the speed
of light, although it might come close. Now an objects length is measured in terms
of the time required by light to travel from one end of the object to the other.
While particles moving slower than that of the speed of light in a vacuum but
quicker than that of light in other mediums, it will emit a faint blue light known
as cherenkov radiation when they pass through the other medium, this phenomenon
has been used in various applications involving elementary particles.